One problem involved with heating of glass sheets is that the edges of the glass sheet tend to become hotter than the center because the edges have a greater surface area for a given square area of the glass sheet surface due to the edge surface that extends between the oppositely facing planar surfaces of the glass sheet. Such edge heating causes warpage of the glass sheet from its planar condition and thereby adversely affects the resultant quality of the glass sheet after subsequent processing. This edge heating problem is present regardless of what type of heating takes place in the furnace whether it is radiant, natural convection, forced convection or any combination of these different types of heating. With roller conveyance of glass sheets, the bottom surface of the glass sheet is also heated by conduction from the conveyor rolls which can also affect the uniformity of the heating.
Prior roller conveyor furnaces for heating flat glass sheets have incorporated heater controls which control the extent of heating along the different lengths of the furnace but have not heretofore addressed the edge heating problem described above.